By studying the phylogenetic history of related species, we can begin to correlate the interplay of behaviors with evolutionary dynamics in the real world. This year scientists from Lund University, in Sweden, analyzed the breeding strategies of 4,000 bird species, tracking their movements into new ecosystems using known genetic relationships between the birds. It’s long been known that cooperative-breeding strategies are common in harsh environments. The assumption was that difficult conditions encouraged species to evolve sociable behaviors (at least toward relatives). But what if this presumed causality had it backward? By analyzing the historical migrations of birds, the researchers discovered that species that had already evolved cooperative behaviors in a benign environment were twice as likely to have moved into a harsh one than non-cooperative breeders. The researchers speculate that cooperation buffers against unpredictable breeding seasons, allowing already social populations to be more successful in invading new niches. The harsh environment didn’t drive the evolution of the behaviors—the behaviors enabled the colonization of harsh environments.

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